This invention relates to an adjustable steering column for a vehicle, and more particularly to the type of column which can be adjusted between several positions of vertical tilt and, within a limited range, between an infinite number of degrees of telescoping or longitudinal extension.
It is known to provide tilting and telescoping steering columns for industrial and agricultural vehicles, as well as for automobiles. Generally, these have been provided for the convenience of the operator. The ability to adjust a steering wheel to various positions of tilt and extension contributes to convenience by allowing operators to adjust for most comfortable steering and for easiest entrance and egress. Different operators may, and often do, prefer different adjustments, or the same operator may prefer different adjustments for different working conditions; for example, he or she may prefer to stand while operating a tractor or other vehicle for one purpose, and to sit while operating it for another purpose.
Unfortunately, the adjustability intended to be provided by tilting and telescoping steering columns of known design suitable for industrial and agricultural vehicles has often been, in important respects, more theoretical than practical. In particular, adjustment between different degrees of telescoping or longitudinal extension has often been difficult for the operator to accomplish. Indeed, such adjustment may be impossible to accomplish without pounding the column with a hammer, heavy wrench, or other implement, to thereby apply brute force to "break" the column away from a locked condition at its then-set degree of telescoping so that it can be shifted and set at another degree of telescoping. At the new setting, the column may again establish a locked condition which will again have to be "broken" by brute force upon subsequent adjustment. Under such circumstances, adjustment may not be worth the bother, particularly where true convenience would require frequent adjustment back and forth between positions.
Examples of prior art columns include Treichel et al. U.S. Pat. No. 3,791,223 and Hansen U.S. Pat. No. 4,257,624. Each of these patents illustrates a telescoping steering column whose length is adjustable over a continuous range between upper and lower limits of full extension and full retraction. In each of these patents, cam surfaces, a wedge nut (82 or 32), and a cooperating shaft member interact to wedge the nut and shaft member against an outer shaft member and lock the linkage in any selected degree of telescoping adjustment. However, such lock may be difficult to "break." It is intended that backing off or rotation of a lock-unlock knob (74 or 40) in the unlocking direction will release the linkage from the locked condition, but when a tight lock exists, the intended result may not occur. Instead, the control rod (72 or 37) may shift axially in such a way as to allow relative movement between the threadedly engaged nut and control rod without releasing the locked condition. The "brute force" approach of pounding or hammering may then be required to break the linkage from its locked condition.